Method for making a casing with protective bellows for transmission device and casing obtained by said method

ABSTRACT

A method for making a casing ( 1 ) with protective bellows ( 2, 2 A) for transmission device, such as a transmission joint, includes at least two shafts mobile axially and/or at an angle relative to each other, the casing ( 1 ) with bellows ( 2, 2 A), whereon at least part of the bellows ( 2 ′) are radial, having at each open end a section ( 3 A,  3 B) for being fixed to the transmission device. The method includes moulding the casing ( 1 ) with bellows ( 2, 2 A), using a hollow mould and at least one core, having each at least a matching helical thread delimiting the moulding space and stripping the casing ( 1 ) formed by relatively unscrewing the casing ( 1 ) and the core to obtain a single-piece casing ( 1 ). The invention is applicable to a casing with bellows by arrangement of extensible or flexible coupling elements.

The present invention relates to a process for the production of acasing with protective bellows for a transmission device, such as atransmission joint, comprising at least two shafts movable axiallyand/or angularly relative to each other, this casing with bellows, forwhich at least one portion of the bellows is radial, having at each openend a securement section to the transmission device, as well as a casingwith protective bellows obtained particularly by the practice of thisprocess.

Different systems for the transmission of movement of a drive shaft to adriven shaft are at present used, preferably with a cardan joint, inparticular in the automotive industry in which more and more uses had,for the drive of the wheels from the motor, to devices with homokineticjoints. In such joint devices, a mechanical assembly is lubricatedpermanently by a mass of grease which is enclosed in a protectivebellows. The latter must be able on the one hand to deform elasticallyin several directions and on the other hand to keep its propertiesdespite multiple causes for damage which can arise in the course of thelife of the vehicle. Thus, it has been known for a long time that damageto the bellows is due in particular to the shocks arising fromprojections of road paving particles which give rise to fissures in theelastomeric material used, or to friction of the elements of the bellowsagainst each other.

There exists in the prior art two types of casings with bellows, namely,on the one hand, casings with protective bellows whose bellows areso-called axial, as shown in FIG. 2, so as to permit essentially a smallaxial deformation of said bellows, on the other hand casings with radialbellows (FIG. 1) permitting radial, axial or angular displacements ofthe transmission device. In the case of axial bellows, the wall of theenvelope is formed by undulations or holes whose flanks extendsubstantially parallel to the longitudinal axis of said casing (see FIG.2). This type of casing has the advantage of being easy to producebecause of the absence of counter-clearances. Thus, for this type ofcasings with bellows, numerous production techniques can be used.However, casings with bellows most often used nowadays are shown in FIG.1 because of their possibilities for deformation. In this case, at leasta portion of the bellows of said casing are radial. In the second familyof casings with bellows, the body of the casing, constituted by atubular body disposed about an axis longitudinal of said casing, isdelimited by an undulant wall whose flanks of the folds extendsubstantially in an essentially radial direction relative to thelongitudinal axis of said wall. This arrangement of folds of the bellowspermits both an axial and an angular deformation of the bellows,rendering such casings with bellows applicable to a large number oftransmission mechanisms.

To permit optimum deformation of such a casing with bellows, thesecasings have for a long time been produced by molding or injection ofvulcanized rubber. However, because of the low mechanical resistance ofrubber, the producers have sought to replace rubber with materials ofgreater rigidity characteristics. As a result, the usual techniqueapplicable to rubber had been replaced by injection/blowing techniquessuch as described in French patent 2.610.566. In addition to the blowinjection technique described in French patent 2.610.566, other blowingtechniques have been developed. Thus, generally and as shown in Frenchpatent 2.606.849, during production, the molding material, constitutedby a thermoplastic elastomeric tube in a pasty condition, is blown. Thethermoplastic elastomer presses itself against the cold walls of themold which represent the external surface of the bellows. Upon opening,the two parts of the mold release the obtained bellows. This blowingprocess represents a complicated and costly mode of production which isnot yet perfected from a point of view of quality. Thus, the correctdistribution of thickness of material along the bellows is difficult toobtain because it depends on a number of factors. As a result, there isrequired on the one hand the use of an excess of material so as toguarantee minimum thickness, on the other hand to provide unitarymonitoring of the pieces.

There are thus sought nowadays processes permitting the production ofcasings with bellows having radial bellows with substantialcounter-clearances and made of a relatively rigid material, inparticular to resist high temperatures and to increase the mechanicalresistance of said casing.

An object of the present invention is thus to provide a process for theproduction of a casing with bellows whose use permits the production byinjection of a casing with bellows having radial bellows of any shape,said casing being obtained from a material of any rigidity adapted toresist in particular high temperatures and adapted to have substantialmechanical resistance.

Another object of the present invention is to provide a casing withbellows whose design permits radial, axial and/or angular deformationsof the bellows without decreasing the lifetime of said casing.

To this end, the invention has for its object a process for theproduction of a casing with protective bellows for a transmissiondevice, such as a transmission joint, comprising at least two shaftsmovable axially and/or angularly relative to each other, this casingwith bellows, of which at least a portion of the bellows are radial,having at each open end a section for securement to the transmissiondevice, characterized in that it consists in molding the casing withbellows, with the help of a hollow mold and at least one core, eachhaving at least one helicoidal complementary screw thread delimiting themolding space, and in demolding the formed casing by relative unscrewingof the casing and the core so as to obtain a single piece casing.

Thanks to the process of production of the casing which comprises a stepof unmolding in the course of which, after opening the hollow mold,there takes place a demolding of the casing by relative unscrewing ofthe casing and the core, there results the possibility of producingcasings with protective bellows of which at least one portion of thebellows is radial, the material used being able to be a material of highrigidity, the bellows being able to take any shape.

The invention also has for its object a casing with protective bellowsfor a transmission device, such as a transmission joint, comprising atleast two shafts movable axially and/or angularly relative to eachother, this casing with bellows, of which at least one portion of thebellows is radial, having at each open end a section for securement tothe transmission device, said casing being preferably obtained by theuse of the mentioned process, characterized in that it is present in theform of a single piece body without an internal axial joint plane, atleast one portion of the bellows being of helicoidal arrangement, thesecurement section of larger dimension having a section for passagegreater than or equal to the diameter delimited by the summit of thebellows of largest dimension.

The invention will be better understood from a reading of the followingdescription of embodiments, with reference to the accompanying drawings,in which:

FIGS. 1 and 2 are fragmentary schematic views in cross-section ofcasings with bellows according to the prior art;

FIG. 3 is a fragmentary partial cross-sectional view of an embodiment ofa casing with bellows according to the invention;

FIG. 4 is a longitudinal half-section of the tool required for molding acasing with bellows according to FIG. 3;

FIG. 5 is a fragmentary cross-sectional view of a casing with bellowscomprising two regions of helicoidal windings of reverse pitch accordingto a modification of the invention; and

FIG. 6 is a fragmentary longitudinal half-section of a casing withbellows in which each bellows is constituted by multiple spiralpassages.

As mentioned above, the invention has essentially for its object aprocess for the production of a casing 1 with protective bellows 2 foran extensible or flexible coupling device, in particular for atransmission device. This casing 1 with bellows 2, 2A, whoseapplications will not be described in greater detail hereafter, isconstituted by a tubular body open at each of its ends and whose wall,arranged about an axis XX′, is, between said ends, undulant over atleast a portion of its length to delimit a plurality of bellows 2, 2A,each fold corresponding to a bellows. The ends of this body, ofgenerally different dimensions, constitute a section 3A, 3B forsecurement to the transmission device. Generally, in the conditionmounted on the transmission device, the securement sections of thecasing are fixed to the device by means of collars, rings or the like.The folds of the body, and in particular the summit of the folds,constituting the rib of the bellows, describe a helix which extends fromone securement section 3A to another securement section 3B about alongitudinal axis of the body. At least one portion of these folds,adapted to constitute the bellows, is shaped so as to form so-calledradial bellows 2. Thus, the flanks of said bellows extend each time in amanner substantially perpendicular to the longitudinal axis of saidbody.

To permit the production of such a casing with protective bellows inparticular radial, there is used, as shown in FIG. 4, a tool constitutedon the one hand by a hollow mold 5, formed for example of two halfshells or a greater number of elements adapted to be brought together todelimit a closed cavity, and at least one core 4. The half shells or thecarcass constituting the hollow mold 5, and the hub or hubs, each haveat least one complementary helicoidal screw thread delimiting themolding space. The demolding of the casing 1 is obtained, after openingthe hollow mold 5, by relative unscrewing of the casing 1 and the core4. There is thus obtained a single-piece casing free from an internalaxial joint plane. This unscrewing can take place in an entirelyautomatic manner. The movement permitting unscrewing of the casing 1from the core 4 is either applied to the core 4 to unscrew the core 4from the casing 1, or to the casing to unscrew the casing from the core.Preferably, the casing 1 is immobilized in the course of unscrewing ofthe core 4. Each time, in this case, the portion which is not subjectedto a drive movement can be held in position for example by means of asuction device, a clamp or the like. In conclusion, the casing and/orthe hub comprises or comprise at least one region adapted either toabsorb a mechanical couple during unscrewing, or permit a blocking inrotation. This zone can be defined by diametrically opposite earsdisposed on the external periphery of said casing. The casing can alsobe unscrewed automatically by application of pneumatic pressure,preferably on a portion between the core and the casing. This pneumaticpressure is transmitted by means of at least one channel passing throughthe molding core.

Generally speaking, the casing 1 is injection molded from athermoplastic elastomer having a hardness preferably at least equal to aShore D hardness preferably at least equal to 60.

To permit demolding by unscrewing, there is selected the largestcross-section of the core or cores 4 to have a diameter less than orequal to the section of passage of the securement section 3A of thelargest dimension of the casing 1 with bellows 2, 2A. According to theshape of the desired casing, there can be given to the core or cores 4and to the body of the mold 5 a truncated conical shape. It is alsopossible to mold the casing 1 with the help of at least two cores 4 eachhaving a helicoidal screw thread of different pitch, even reversed,preferably increasing in the direction of the portion of the coreadapted to extend adjacent the section 3A for securement by the largestdimension of the casing 1. To facilitate demolding, the largestcross-section of the first core is less than the smallest section of thesecond core. There is thus obtained a casing which can be like thatshown in FIG. 5 in which the pitches are oriented in opposite directionfrom one core 4 to another. It is also possible to select a coredelimiting the spiral passages of the bellows, of increasing width fromthe smallest securement cross-section 3B toward the largest securementsection 3A. This width can thus develop up to 15% per turn of the screwthread. It will generally increase from 1 to 3% per turn of the screwthread.

Of course, as a function of the shape of the helicoidal screw threadsprovided on the core 4 and the mold 5, a large number of shapes can beobtained for the bellows 2 of the casing 1. One embodiment is shown inFIG. 6. The production of such a casing by injection also permitscausing to vary as desired the thickness of said walls of the bellows 2.Thus, each bellows can have a reinforced zone, or conversely a thinnedzone, at the junction of one bellows with an adjacent bellows in thehollow region between two bellows. It is also possible to providebellows whose flanks are constituted on one surface to be concave and onthe other surface to be convex. This will result in greater clearancesof the spiral.

The casings 1 with bellows 2, 2A which result from such a productionprocess can have a large number of shapes. Each casing 1 however willhave the form of a single-piece body free from an internal axial jointplane. This casing is constituted by a tubular body disposed about anaxis XX′ and whose ends are open. Each open end is adapted to constitutea section 3A, 3B for securement of the casing 1 to the transmissiondevice. This tubular body of the casing is delimited over at least oneportion of its length by an undulated or folded wall. Each foldcorresponds to a bellows. The folds or ribs of the bellows between saidsections 3A, 3B can thus describe a helix of constant or variable pitch,preferably increasing in the direction of the section 3A of largest sizefor securement of the casing 1. In the example shown in FIG. 3, thehelix has an angle α corresponding substantially to the angle formed bythe axis of the fold constituting the radial bellows with an axisperpendicular to the longitudinal axis XX′ of the body. These folds canbe oriented such that the flanks of the folds extend substantiallyradially relative to the longitudinal axis of the body of the casing oraxially relative to this latter. A combination of the two can also beobtained as shown in particular in FIG. 3. Independently of the numberof radial bellows with helicoidal arrangement or of axial bellows 2A, itis fundamental that the section 2A for the largest securement section ofthe casing 1 have a passage section greater than or equal to thediameter delimited by the summit of the largest bellows. Thus, in theexample shown in FIG. 3, reference B corresponds to the radius of thelargest bellows whilst reference A corresponds to half the cross-section3A for securement of the largest in its size. A is thus necessarilygreater than B.

According to the forms of the cores 4 and the hollow molds 5 they use,the bellows 2, 2A can be of identical diameter for the production of acylindrical casing. However, in a preferred arrangement of theinvention, the bellows are, from the section 3B of smallest dimensiontoward the section 3A of largest dimension, of progressive diameter,enscribed in a truncated cone. The radial bellows 2 can be constitutedby single or multiple spiral passages. FIG. 6 shows an example in whicheach bellows 2 is constituted by two successive folds of differentshapes. It is to be noted that, to reduce the time of unscrewing of thecasing 1 with bellows 2 during the demolding phase, it is preferable tohave a large helical pitch. But the greater the pitch, the fewer will bethe spirals along a same length of bellows. However, the flexibility ofthe bellows increases with the number of spirals. Thus, to preserveflexibility by having a large pitch, it is preferable to arrange on thebellows at least one supplemental screw thread of spirals. Each screwthread can thus have its own shape of spiral.

In the case of a bellows having several spiral screw threads, thesescrew threads can be provided with different sizes of spirals. It isthus possible to have a change in the level of the hollows and the peaksof the spirals. Thus, thanks to the mentioned production process, thecasing with bellows can comprise, at the level of the bellows, bellowswhose spirals form different helicoidal spirals either at the level ofthe profile for the production of the spirals, or as to the size of thespirals, namely as to the pitch of the helix, or else as to theorientation of this pitch. Of course, these factors can be combined.There results a large number of possible embodiments for said casings.

In the particular case of the casing with bellows comprising two zonesof helicoidal spirals with reverse pitch from one zone to the other, thecore is constituted by two elements. The second element of the corecorresponding to the region of spirals of reverse pitch unscrews in theopposite direction from the first element during unmolding of thecasing. The interest of having on the casing with bellows, regions ofspirals of reverse pitch, is to be able to compensate the effect oftwisting of one zone by the other zone which has the tendency to twistin the opposite direction. Thus, the helicoidal spirals tend to twistthe bellows of the casing when they are stretched or compressed. Theeffect of twisting the bellows of the casing can be minimized bysuitable distribution of the thicknesses of the spirals.

Such a casing 1 with bellows could be disposed in the conventionalmanner on a transmission mechanism. The securement of the section 3A oflargest dimension of the casing 1 with bellows is generally designed toensure complete sealing. Thus, generally the grease contained within thecasing with bellows is projected toward the securement section 3A ofgreat dimension by the action of centrifugal force. The securement ofthe section 3B of least dimension is provided to be sealed to grease butcan let air pass and can permit a slight movement of rotation so as tocompensate the twisting of the bellows of the casing. The bellows canthus comprise for this purpose a helicoidal lip. Each securement section3A, 3B of the casing 1 can also be constituted by at least twobi-injected materials. Thus, a thermoplastic elastomer can be injectedwithin the securement section of largest dimension to obtain bettersealing. One of the injected materials can be a material adapted toreflect thermal radiation such that at least a portion of the casing iscovered with a reflective coating.

1. Process for the production of a casing (1) with protective bellows(2, 2A) for a transmission device, such as a transmission joint,comprising at least two shafts movable axially and/or angularly relativeto each other, this casing (1) with bellows (2, 2A), of which at least aportion of the bellows (2) is radial, having at each open end a section(3A, 3B) for securement to the transmission device, characterized inthat it consists in molding the casing (1) with bellows (2, 2A), with ahollow mold (5) and at least one core (4), each having at least onecomplementary helicoidal screw thread delimiting the molding space, andin demolding the formed casing (1) by relative unscrewing of the casing(1) and the core (4) so as to obtain a single-piece casing.
 2. Processfor production of a casing (1) with protective bellows (2, 2A) accordingto claim 1, characterized in that the casing (1) is injection moldedfrom a thermoplastic or a thermoplastic elastomer.
 3. Process forproduction of a casing (1) with protective bellows (2, 2A) according toclaim 1, characterized in that the largest cross-section of the core orcores (4) is arranged have a diameter less than or equal to the passagesection of the securement section (3A) of largest dimension of thecasing (1) with bellows (2, 2A).
 4. Process for the production of acasing (1) with protective bellows (2, 2A) according to claim 1,characterized in that there is given to the core or cores (4) and to thebody of the mold (5) a truncated conical shape.
 5. Process for theproduction of a casing (1) with protective bellows (2, 2A) according toclaim 1, characterized in that the casing (1) is molded with at leasttwo cores (4) each having a helicoidal screw thread of different pitch,preferably increasing in the direction of the portion of the coreadapted to extend to adjacent the securement section (3A) of largestsize of the casing (1).
 6. Casing (1) with protective bellows (2, 2A) ofa transmission device, such as a transmission joint, comprising at leasttwo shafts movable axially and/or angularly relative to each other, thiscasing with bellows, of which at least one portion of the bellows isradial, having at each open end a section (3A, 3B) for securement to thetransmission device, said casing (1) being obtained particularly by thepractice of the process according to claim 1, characterized in that itis in the form of a single-piece body free from an internal axial jointplane, at least one portion of the bellows (2) being of helicoidalarrangement, the securement section (3A) of largest size having apassage section greater than or equal to the diameter delimited by thesummit of the largest bellows.
 7. Casing (1) with bellows (2, 2A) forprotecting a transmission device according to claim 6, characterized inthat the radial bellows (2) are constituted by single or multiple spiralpassages.
 8. Casing (1) with bellows (2, 2A) for protecting atransmission device according to claim 6, characterized in that thebellows (2, 2A) are of identical diameter for the production of acylindrical casing.
 9. Casing (1) with bellows (2, 2A) for theprotection of a transmission device according to claim 6, characterizedin that the bellows (2) are of progressive diameter inscribed within atruncated cone.
 10. Casing (1) with bellows (2, 2A) for the protectionof a transmission device according to claim 6, characterized in that thetubular body of the casing is delimited over at least a portion of itlength by an undulant or folded wall, each fold corresponding to abellows, the folds describing a helix of constant or variable pitch,preferably increasing in the direction of the securement section (3A) oflargest size of the casing.
 11. Casing (1) with bellows (2, 2A) for theprotection of a transmission device according to claim 6, characterizedin that the casing (1) comprises axial bellows (2A) and radial bellows(2).
 12. Casing (1) with bellows (2, 2A) for the protection of atransmission device according to claim 6, characterized in that eachsecurement section (3A, 3B) of the casing (1) is constituted by at leasttwo bi-injected materials.